The test is performed over a serial link to an LS1043A processor. A write command is issued in Uboot then a read command to verify the address contains the data just written. This test successfully passed multiple times at different temperature levels, before ceasing.

While testing are you always under datasheet operating conditions for the device. Also is the device power cycled in between ? It can happen that the device is not getting powered up correctly. Are your rise times and fall times for the input and power supply below 1.8 ns ?

We are testing the device under datasheet operating conditions. The power supply rise and fall times are within the specified limits. The device is powered during the temperature cycles. I would like to review the device reliability data and recommended thermal profile for solder/reflow. The manufacturer's web site is woefully lacking direct support.